Avast has stopped working, what should I do?

Hello all,
I have the freeware version of Avast (6.0.1367) on a Win XP SP3 operating system. Yesterday, completely out of the blue, the system tray icon had a red cross in it.. uh oh trouble!. I clicked to see what the error was, "Urgent: Avast service stopped or is in an inconsistent state".
There were two options given to me which were – 'Fix Now' button and a 'Start program' link, I tried clicking both of these buttons but neither led anywhere or did anything.
I am either going to reinstall avast or do a system restore but just thought I would get your advice first. Thank you in advance for any advice.
